⑴ Monochrome ballpoint pen: This is the most common ballpoint pen, often in blue, black, red, etc.
⑵ Two-color ballpoint pen: generally red and blue two-color.
⑶ Three-color ballpoint pen: red, blue and black.
⑷ Four-color ballpoint pen: red, blue, black and green. In addition to these four, there are six-color, eight-color, and even twelve-color ballpoint pens.
